High intensity discharge (HID) lamp fixtures are widely used to provide lighting in warehouses, airplane hangars, and other commercial buildings. Typically, fixtures using such lamps use mercury vapor, metal halide, and high or low pressure sodium lamps, depending upon the particular application and the lighting characteristics desired. Such lamps generally are high wattage (500 or 1000 Watts, for example); so that in the buildings in which they are used, significant energy consumption takes place.
For the purpose of maximizing the downward light output from such high wattage lamps, flared, generally bell-shaped reflectors have been designed to fit over the base of the bulb, which then is screwed into the power supply outlet for the lamp. The lamp itself, in at least some of these applications, forms the support for the reflector, which generally is made of polished aluminum or similar lightweight material. The lamp extends through the base end of the reflector; and the light-emitting end is either open or covered with a translucent lens to disperse the light emanating from the lamp, and to provide a more attractive appearance.
The coverage or area of illumination of a typical reflector for an HID lamp of this type generally is approximately 1.6 (that is, it is 1.6 times the height from the floor to the light-emitting opening of the fixture). The light typically is projected in a circle; so that the spacing of the lamp fixtures is selected in accordance with this formula to provide the desired amount of overlap, if any, needed for any particular application.
A primary problem with HID lamps, of any of the above types, is that the high wattage results in significant energy consumption, which, in turn, translates into high utility bills. Fluorescent lamp fixtures typically are low wattage fixtures; but for providing the desired levels of illumination in warehouses, airplane hangars and similar high-ceilinged buildings, a large number of fluorescent light fixtures must be employed to produce the desired lumens of light on the floor of the building in which they are used. The large number of fixtures required results in significantly increased initial installation cost over the fixtures required for HID lamps, typically spaced greater distances apart in a comparative installation. In addition, many applications indicate that standard fluorescent lamp fixtures cannot produce the necessary lumens of light at the floor or work surface of warehouses and the like.
High intensity discharge lamps of the mercury or metal halide variety utilize gas in a discharge tube, which is manufactured from quartz. Current passing through the gas generates light. The discharge tube is enclosed in an outer bulb which is formed from glass. Consequently, the light passes through both the quartz discharge tube and the glass bulb. The discharge tubes of these lamps emit a high degree of ultraviolet radiation along with the light.
Normally, this is not of any consequence, since ultraviolet radiation in the harmful ranges is absorbed by the outer glass bulb. In a sports area, however, it is possible (and has been known) for a ball or other object to hit a HID fixture, breaking the outer bulb but leaving the structurally stronger quartz arc tube intact. In such an event, the HID lamp continues to burn; and ultraviolet radiation of harmful wavelengths is emitted directly, and is likely to strike players or spectators. The results can be unpleasant and potentially dangerous in severe cases. On the other hand, the light generated by fluorescent lamps contains no significant ultraviolet radiation. Although some ultraviolet radiation is produced within the fluorescent tubes, the ultraviolet radiation is absorbed by the glass tube. If the tube is broken, the lamp immediately extinguishes, and there is no danger from the damaging effect of uncontrolled ultraviolet radiation.
Generally, commercial ceiling lamps for fluorescent light fixtures employ elongated fluorescent tubes, usually having a length of four or eight feet. These tubes then are placed in appropriate luminaires oriented parallel to the floor or ground to produce the desired illumination. Installation and replacement of fluorescent tubes, particularly eight foot tubes, is somewhat difficult simply because of the length of the tubes involved.
Compact fluorescent tubes have been designed in a generally "folded-over" configuration, which attach to a light fixture at one end. Three patents disclosing ceiling light fixtures for recessed lamp reflectors, and which use compact fluorescent tubes, are the U.S. Pat. Nos. 4,520,436; 4,704,664; and 4,922,393 to McNair. These patents disclose the use of a pair of compact fluorescent lamps, mounted in a generally crossed configuration inside a dome-shaped reflector, to produce a light output which is comparable to that of an incandescent bulb in a reflector having a similar diameter light-emitting end. The reflector, itself, is designed with openings through it, in which the bases of the lamps are mounted (on the upper outside of the reflector). Provisions also are made for attaching the ballasts for the lamps to the outside of the reflector. The reflector then is placed in a recessed housing in the ceiling to accommodate all of the lamp sockets and ballasts in a space between the reflector and the end of the housing.
In the devices shown in all of these patents, the housing itself has a threaded lamp base on it to supply operating current to the ballasts and the lamps. The conventional screw-in threaded base then may be inserted into a normal incandescent lamp socket; so that the entire housing is suspended from the socket. These fixtures are designed to replace incandescent lamps in recessed ceiling fixtures of relatively low wattage (typically replacing a 60 to 100 Watt incandescent lamp). Lower power consumption results; and the lumen output, using crossed pairs of compact fluorescent lamps, is approximately equivalent to the incandescent lamp replaced. In addition to reduced power consumption, the compact fluorescent lamps typically have a life several times greater than the life of incandescent lamps.
A different approach to a lighting apparatus is disclosed in the British patent to Schmidt No. 878,534. Schmidt is directed to a very specific three-phase lighting apparatus, where each of three lamps (which may be incandescent lamps or mercury vapor lamps) are operated from a different one of the three phases of an electrical supply. As noted in Schmidt, this causes a stroboscopic effect from each individual one of the light sources; but the overall effect from the fixture itself is one of relatively uniform light supply. The Schmidt apparatus comprises a lamp base with three fairly closely spaced sockets in it. The sockets extend outwardly at angles of approximately 45.degree. relative to the vertical; and the lamps are clustered in the center of the fixture, spaced a substantial distance from the reflector which surrounds them.
It is desirable to provide a lighting apparatus which may be directly substituted for high-wattage HID lamp fixtures, or, alternatively, which may be directly substituted for HID lamps as a direct replacement, which provides the advantages of reduced power consumption, which is relatively inexpensive and which produces a lumen output comparable to the high-wattage HID lamps being replaced.